Tosylhydrazone – neue Anwendungen klassischer Reagentien in palladiumkatalysierten Kreuzkupplungen und metallfreien Umsetzungen

Abstract

Tosylhydrazone sind wertvolle Zwischenverbindungen, die in der organischen Chemie seit fast 60 Jahren Anwendung finden. Die jüngste Entdeckung einer palladiumkatalysierten Kreuzkupplungsreaktion unter Beteiligung eines Tosylhydrazon‐Kupplungspartners weckte ein neues Interesse an diesen Reagentien. Die Reaktion ist nahezu universell für Hydrazone und kann zur Synthese polysubstituierter Alkene genutzt werden. Im Verlauf dieser Forschungen wurden außerdem neue metallfreie C‐C‐ und C‐O‐Kupplungen gefunden. Da Tosylhydrazone leicht aus Carbonylverbindungen zugänglich sind, bieten diese Umwandlungen neue Möglichkeiten für die Derivatisierung von Carbonylverbindungen. Dieser Kurzaufsatz behandelt diese neuartigen Reaktionen dieses klassischen Reagens.

Palladium‐Catalyzed Divergent Reactions of α‐Diazocarbonyl Compounds with Allylic Esters: Construction of Quaternary Carbon Centers

“…Generation of a palladium carbene species (A), followed by the migratory insertion of an aryl, [6] benzyl, [7] vinyl, [8] allyl, [9] acyl, [10] alkynyl, [11] or allenyl [12] group, gives rise to the alkyl-palladium complex (B). In most cases, this complex undergoes b-hydride elimination to afford an olefin [5] (Scheme 1, pathway a). Alternatively, intermediate B can undergo transmetalation followed by reductive elimination to form two different CÀC bonds at the same carbon atom in a single reaction [6g, 13] (Scheme 1, pathway b).…”

“…[4] Recently, palladium-catalyzed cross-coupling with diazo compounds as nucleophilic coupling partners has been introduced as a new method for the formation of CÀC bonds. [5] The characteristic steps of the mechanism that differentiate it from traditional cross-couplings are shown in Scheme 1. Generation of a palladium carbene species (A), followed by the migratory insertion of an aryl, [6] benzyl, [7] vinyl, [8] allyl, [9] acyl, [10] alkynyl, [11] or allenyl [12] group, gives rise to the alkyl-palladium complex (B).…”

Luxury of N‐Tosylhydrazones in Transition‐Metal‐Free Transformations

“…Thet ransition-metal-freec ycloaddition approach was furtherd eveloped by Va ldØsa nd co-workers for the regioselective synthesiso fp yrazoles (99 and 100) via a[ 3 + +2] cycloaddition followed by [1,5]-sigmatropic rearrangement sequence (Scheme 40). [47] Va rious alkyl (Me/n-Pr/Et)and aryl ketone-derived N-tosylhydrazonesa nd terminal alkynes( aryl/heteroaryl/alkyl) were successfully used to construct 3,4,5-trisubstituted pyrazoles with aw ide scope.T he synthesis of 1,3,5-trisubstituted pyrazoles 99 was also demonstrated by the reactiono fb enzyl-containing hydrazones with aryl-/ Scheme 39.…”

“…heteroaryl-derived terminal alkynes.M oreover, the reactionw ith the tosylhydrazone of cyclick etones afforded the carbocyclic fused pyrazoles by a[ 3 + +2] cycloaddition/ [1,5]-sigmatropic rearrangement/ring expansion sequence. Synthesis and scope of the pyrazoles by the Va ldØsapproach.…”

“…[1] Because of their wideranging reactivities,the literature continuestoprovide evidence of their potential to buildd iverse molecular frameworks. [1] Because of their wideranging reactivities,the literature continuestoprovide evidence of their potential to buildd iverse molecular frameworks.…”